Harrison was an influential writer & autodidact; his Wikipedia page states that he "profoundly influenced a generation of 'New Negro' militants, including A. Philip Randolph, Chandler Owen, Marcus Garvey, Richard Benjamin Moore, W. A. Domingo, Williana Burroughs, and Cyril Briggs."
When Africa awakes: The "inside story" of the stirrings and strivings of the new Negro in the Western world
https://www.gutenberg.org/ebooks/69712
The Negro and the nation
https://www.gutenberg.org/ebooks/69835